Question

Which statement correctly describes whether a compound is a pure substance? A compound is not a pure substance because each of its molecules is made up of the atoms of two or more different elements. A compound is a pure substance because its molecule cannot be broken down into simpler particles by physical means. A compound is not a pure substance because it is not an element, and only elements are pure substances. A compound is a pure substance because it consists of two different elements, which are pure substances.

Answer 1

1. ANSWER:B
2. i take the test

Answer 2

Answer is: A compound is a pure substance because its molecule cannot be broken down into simpler particles by physical means.

Pure substance is made of only one type of atom (element) or only one type of molecule, it has definite and constant composition with distinct chemical properties. Pure substances can be separated chemically, not physically, that is difference between pure substances and mixtures.

Electrolysis of water (pure substance) is the chemical separation, because from one molecule (water) two molecules (hydrogen and oxygen) are produced. Water is separeted into two molecules:

Reaction of reduction at cathode: 2H⁺(aq) + 2e⁻ → H₂(g).

Reaction of oxidation at anode: 2H₂O(l) → O₂(g) + 4H⁺(aq) + 4e⁻.